Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Emerging radio frequency communication standards expand capacity by defining secondary users. Primary users preemptively operate on defined bands and sub-bands according to present rules. Secondary users, in contrast, are allowed to use spectrum only after sensing that the spectrum is available in a process termed “cognitive radio.” Cognitive radio devices need to be able to efficiently and quickly sense a given portion of the radio spectrum in order to determine which regions of the spectrum are available for use so as not to interfere with primary users.
Because cognitive radios are considered lower priority or secondary users of spectrum allocated to a primary user, a fundamental requirement is to avoid interference to potential primary users in their vicinity. On the other hand, primary user networks have no requirement to change their infrastructure for spectrum sharing with cognitive networks. Therefore, cognitive radios should be able to independently detect primary user presence through continuous spectrum sensing.
Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. This concept in data communication is based on allowing several transmitters to send information simultaneously over a single communication channel. Several users are thus enabled to share a bandwidth of different frequencies referred to as multiplexing. CDMA may employ spread-spectrum technology and a special coding scheme, where each transmitter is assigned a code to allow multiple users to be multiplexed over the same physical channel. CDMA is a form of spread-spectrum signaling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
The present disclosure appreciates that there are several limitations with designing cognitive radio systems. For example, cognitive radio devices need to independently and rapidly detect primary user presence on a channel in order to use that channel. On the other hand, size and cost considerations are a significant aspect of electronic communication devices today. Devices such as wireless communication modules, portable computers, and comparable ones are progressively designed with smaller form factors and lower manufacturing costs. Thus, implementing cognitive radio in widely available consumer devices is a complex undertaking.